What grade of gas does everyone run in their 240 EFI, I ran regular all last summer because I have never heard any different? Should I be running premium? Is there any literature that states what we should be running in this motor?

I doubt you will find anything that is proven one way or the other, but they both have their pros and cons. I am sure you know what they are so I won't bother with them but I am always looking to squeeze as much performance out of what I am driving as I can...!!!

I have had a tank or 2 of "bad" gas using regular in the past. Not in the boat, but in the truck. Runs like crap, sputters...etc etc.... Depends on who's Gas it is....

What grade of gas does everyone run in their 240 EFI, I ran regular all last summer because I have never heard any different? Should I be running premium? Is there any literature that states what we should be running in this motor?

What grade of gas does everyone run in their 240 EFI, I ran regular all last summer because I have never heard any different? Should I be running premium? Is there any literature that states what we should be running in this motor?

I use premium, It does help a little. Cant say much for the boat because thats all I have ever put in it. I can tell the diff In my quad. So thats all I use now for everthing, and thear is a lot of gas thats crap theas days. Every book I have read about any thing says 87 and up.

Just thought I would throw my two cents into the mix -- I am a Shop Foreman and licenced technician at a GM dealership (so a certified gearhead). I have been sent on countless courses concerning drivability of our cars and things that affect it, and one of the concerns which always comes up is fuel. The manufacturer designes and builds engines and fuel injection systems with a particular thing in mind, be it the oil (TCW-3 or not etc.) or the fuel, coolant, or whatever. If the manufacturer designed their engine to run on 87 octane fuel, this fuel will work the best in that engine, performance wise at least.
I don't know how much everyone knows about octane, so I will tell you briefly what it means pertaining to what octane you should use in your engine. Fuel with a lower octane rating has actually more heat energy, or BTU's in it. Heat energy is what pushes your piston down and gives you power so it would seem that less octane is better. Yes, but lower octane fuels are less stable and burn with more of a bang than a controlled burn you would get with a higher octane fuel. This is where preignition (pinging, spark-knock etc.) come in. So as the octane level of the fuel goes up, the fuel has a more controlled, slow complete burn, but with less overall BTU's.
That is why high performance race engines with very high compression must use very high octane fuel. The fuel must be stable enough not to ignite under the intense heat of compression. (My dad's drag racing snowmobile has to use minimum 112 octane fuel to keep from burning pistons)
On the other side of that, my Suzuki Hayabusa GSX1300R motorcycle calls for 87 octane fuel, and it makes 4 more horsepower with that than on 92 octane fuel (same brand). This was tested by me on a rear wheel dyno at a bike shop in my area.
So by this math, if Merc designed their engine and injection system to use 87 octane fuel, this is the fuel that you will get the most power with. The ony other thing to think about is that with mid grade or premium especially, you are buying the cleaning additives in the fuel as well as built in preignition protection. There are very few cleaning additives in regular fuel to keep your injection system clean, and if the fuel gets stale and loses an octane count or two, you could have some preignition and start to damage the tops of your pistons.

Hope that helps and doesn't confuse anyone worse! If anyone thinks I didn't make any sense, let me know and I will try to explain better.